1. Field of the Invention
The present invention relates generally to architectural renderings, and in particular, to a method, apparatus, and article of manufacture for simulating a natural watercolor filling with realistic edge darkening in an architectural rendering.
2. Description of the Related Art
In the architectural, engineering, and construction (AEC) fields, computer aided design (CAD) drawings are often used to design blueprints, drawings, plans, etc. However, such CAD drawings may be complex, confusing, and fail to provide an end-user (e.g., a potential client) with a drawing or visualization of the “intent” of the architect or designer. Architectural renderings are designed to illustrate the “intent” of the designer or architect, as opposed to showing precise fidelity. In these renderings, the illustrator may want the inside of an object (referred to as fill) to appear natural. Prior art applications may attempt to provide such a natural appearance by modeling natural media materials and fills, such as those made be watercolor. However, accurately simulating watercolor may be difficult and/or consume extensive processing power. Such problems may be better understood with a description of prior art drawing software and methodologies.
CAD programs provide high fidelity drawings that fail to provide a visualization of the intent of the user. Such CAD programs or other drawing programs may be vector-based or raster-based. It may be possible to achieve hand-drawn effects in raster-based drawing programs. For example, in a raster-based paint program, a bitmap stroke may be created that appears hand-drawn (e.g., using a variety of raster-based drawing/paint tools). However, it may be preferable to work in a vector-based drawing. For example, in vector-based drawing programs, a user may work with modifiable shapes that can be edited, resized, and rearranged. Nonetheless, the inherent mathematical description of vector shapes lends itself to the production of hard-edged, non-organic artwork. Thus, it has always been a challenge for digital artists to achieve natural hand-drawn effects in a vector-based drawing program.
While the prior art has attempted to create vector-based strokes that appear organic, the prior art has failed to make object fills appear natural. For example, prior art programs may attempt to fill an object utilizing a single Bezier curve that wraps back and forth from one side of a shape to the next. Such a technique utilizes a single stroke and does not appear authentic or hand-drawn. Instead, the single Bezier curve appears computer generated. Another prior art technique may define a shape using a Bezier curve and utilize the defined shape as the paint stroke. For example, if a rectangle is defined, as the user draws the stroke and presses harder (e.g., using a stylus and tablet device), the rectangle deforms in relation to the pressure. However, the shape or stroke or pressure cannot be modified after it is drawn.
In view of the above, fills, in general, are typically either solid/transparent color, images or patterns. Such prior art fill techniques fail to achieve an easy, intuitive, vector-based modifiable means for providing a hand-drawn look of natural art tools.
In particular, prior art techniques have failed to achieve a fast efficient mechanism for creating and displaying a watercolor fill in a vector based environment. A number of commercial and academic efforts have been made in the area of watercolor rendering. One example of such a commercial effort is Painter™ from Corel Corporation™. The academic efforts have concentrated on performing a fluid simulation in order to approximate the water and pigment distribution on paper. Such efforts are more accurately described in the following articles that are incorporated by reference herein:
Curtis, C. J., Anderson, S. E., Seims, J. E., Fleischer, K. W., and Salesin, D. H. 1997. Computer-generated watercolor. In Proceedings of the 24 th Annual Conference on Computer Graphics and interactive Techniques International Conference on Computer Graphics and Interactive Techniques. ACM Press/Addison-Wesley Publishing Co., New York, N.Y., 421-430 (1997); and
Tom Van Laerhoven, Jori Liesenborgs, Frank Van Reeth, “Real-Time Watercolor Painting on a Distributed Paper Model,” cgi, pp. 640-643, Computer Graphics International 2004 (CGI'04), 2004.
In this regard, prior art techniques attempt to perform a fluid simulation to simulate how the water and pigment is distributed over a drawing page. For example, a drawing page may be divided up into cells and analyzed from one cell to another cell to determine the amount of water and pigment that is transferred between cells. However, calculating the watercolor using a fluid simulation is time intensive and, even when performed in real-time, will often only work on limited resolution bitmaps. Further, such fluid simulation does not scale well.
Accordingly, what is needed is the capability to simulate watercolor in a vector based computer application that is efficient, can be performed in real-time, and scales well.